This invention relates generally to an air pressure type fire sprinkler system and more particularly to a liquid detector located in the drum drips of such a system. Many fire protection systems now in use employ a plurality of thermally operated sprinkler heads connected to a piping network located in an elevated position in the space which is to be protected. In response to a local ambient temperature above a predetermined level, individual heads actuate and discharge water or other liquid in the immediate vicinity. When the system is filled with water, the response is rapid after one or more of the sprinkler heads are actuated by elevated temperature.
However, in low temperature environments such as in food warehouses, freezers, and the like, it is undesirable to maintain water in the piping network except during emergencies because stagnant water will freeze and cause blockage or actual physical damage to the system. To overcome this difficulty, systems are filled with pressurized gas instead of water. When a sprinkler head is actuated by elevated temperature and opens, gas pressure is lost and a pressure sensitive device triggers a water valve which then fills the system with water directed to the actuated sprinkler head.
Unfortunately, the practical problems of an actual system for a cold ambient are not entirely resolved by the air pressure type fire sprinkler system because some liquid and moisture is always present in the pipes and in gas which pressurizes the pipes. Under sufficiently cold ambient conditions, the moisture condenses within the piping system and, as liquid, is subject to freezing whereby the piping system is jeopardized. A ruptured pipe causes a loss of gas pressure, triggering the water valve and causing a discharge of water with a potential for physical damage of goods and property.
Commercial fire sprinkler systems of the dry air type, that is the air pressure type, are provided with low end drains known as drum drips. These drum drips are substantially vertical pipes connected to the overhead piping and positioned such that residual and condensate in the pipes will drain into the drum drips which are fitted with gate valves at their lower ends. Periodically, the gate valves are opened and accumulated water and condensate may be removed. Otherwise, the drum drips themselves are in danger of being ruptured if freezing occurs even though the water collected therein is a small quantity. Rupture of a drum drip in an air pressure system will produce a false fire indication and actuation of the water valve which in turn will result in flooding the space which is protected by the sprinkler system. Because the sources of the water in the drum drips are so variable, that is, condensation, and moisture in the gas supply, it is difficult to know when the drum drips need to be emptied.
What is needed is a detector for liquid in the drum drips which is actuated by the presence of accumulated water and thus provides an indication of this presence. Then the drum drip can be emptied before a dangerous condition is produced.